Methods are known for synthesizing musical tones by means of modelling and reproducing the vibrational modes of various musical instruments. For example, to simulate the decaying sounds of a plucked string instrument, such as guitars, or of a struck string instrument, such as pianos, a closed-loop electric circuit can be used, consisting of a delay simulation circuit to represent the propagation modes of vibrating strings, and a low-pass filter circuit to represent acoustic decay of vibrating strings.
When such a circuit is excited with an input signal, representing an impact of a hammer striking a string, the excitation signal can be made to loop around the circuit to simulate the resonance vibration of the string. In such a circuit, the excitation signal undergoes decay, caused by the action of low-pass filters, to simulate the natural decay of a sound of an activated string. The decayed signal can be reproduced electrically to generate a musical tone to simulate the type of sound made by the natural instrument. Such techniques are disclosed in Japanese Patent Application Laid-Open Nos. S52-73721 and S63-40199.
In real situations, however, the natural musical tone colors generated by natural instruments display a variety of tone envelopes depending on the initial and residual touching modes, in the case of pianos and likewise for guitars, depending on such factors as the manner of plucking and the hardness of a pick.
Therefore, the present technology of simple adjustments of low-pass filters in a closed-loop circuit is inadequate for faithful reproduction of complex tone envelopes generated by natural instruments.